Mike Mahoney 40 Degree Bowl Gouge

[Michael Ginsberg]

Need opinions. Mike Mahoney advocates a 40 degree bevel angle on his swept back bowl gouge. Obviously he is well respected and I value his opinion, but I have been using what I considered to be a normal 60 degree bevel angle with success. What do all of you think?
Thanks for your input.

[Dennis Ford]

I have a D-Way gouge ground at ~40 deg and really like it for the outside of bowls, HFs etc. The aggressive angle is a little harder to control but it excels at removing wood in a hurry. It also works very well for finish cuts when used at a high shear angle.

[Steve Schlumpf]

My Thompson 5/8" V gouge is fairly swept back and the nose angle is very close to 42*. It's all in what you get used to using...

[Wally Dickerman]

Actually, there isn't a standard grind for bowl gouges. Yes, many do use a 60 degree grind, but some big name turners use a 40 deg. grind. Mahoney and Stuart Batty for instance. But they also use grinds closer to 60 deg for inside bowl bottoms etc. Just depends on what you turn and what works for you.

In my own turning my 1/2 inch gouges (5/8 US) are ground at 60 deg. I have a 3/8 in gouge ground at around 50 deg. and I have a 1/4 in. gouge ground at a little less than 45. They are all used in different ways. My 1/4 in gouge is used as a detail gouge and sees a lot of use.

[Mark Levitski]

The aggressive angle is a little harder to control

If your rubbing the bevel or close to it, the 40* angle will not be more aggressive compared to a 60. Only the direction of the handle changes. That is why the 60* is easier to use inside bowls, and the 85* even better. If you have a bevel angle too flat (i.e., closer to parallel with the shaft/handle) the handle of the gouge will hit the side or rim of a bowl as you turn the corner into the bottom at the same time rubbing the bevel.

[Bernie Weishapl]

I am kinda like Wally in that I have 3 of the 1/2" gouges with a 60*, 50* and 40* bevel that are swept back that are all used at different times.

[Harry Robinette]

When we spent the day with Stewart Batty he said he used the 40* for the transition from the side to the bottom. It's so the bevel will slide across the wood and the heal of the bevel wont pick up the edge when it hits the wood. I've had one shaped this way ever sense and yes it really helps.

[Michael Ginsberg]

Thanks All! That is what I needed to hear. Appreciate it.

[Reed Gray]

I recently picked up Mike's new video on making heirlooms. Good video. He doesn't use a swept back grind like the Ellsworth type gouge. He and Stewart both prefer a 40 degree bevel, and 40 degree sweep to the gouge, which incidentally is the same angle of a beaver's tooth bevel. For his finish cuts on the inside of the bowl, he uses a 'traditional' grind gouge. This is one I will have to ponder a bit, and am not really familiar with. The profile is closer to a spindle roughing gouge, almost straight across the top of the gouge, with almost no sweep, and just about the same 40 degree bevel. He cuts just slightly on the uphill/bowl side of the gouge, with the flutes almost vertical. This is not a cut you can do with a swept back gouge, and it gives a high shear angle for a very clean cut. Steeper bevel angles are better on the inside of the bowl where tool access is determined by how shallow or deep your bowl is. 45 degree bevel will do fine in a cone shape 12 inches wide, and 6 inches deep. When you add a curved side to the bowl and the transition area in the bottom, you can't do a bevel rubbing cut from rim to bottom center unless you have a steeper bevel. I have most of my gouges ground to about 55 to 60 degrees, and a couple that are closer to 80 degrees for going across the bottom.

robo hippy

[Michael Ginsberg]

Thank you Reed,
It looks like the way to go is have three bowl gouges of various grinds with different angles. A question for you.. For your 80 ish degree gouge.... do you grind to a conventional grind or a swept back? I had no trouble grinding the tradional grind on the Wolverine platform, but the sweptback was a risky operation using the Vari-Grind jig. I had to use a very light touch because of the steep angle as it kept wanting to slip under the wheel.
Michael

[Reed Gray]

I do all my sharpening on a platform, and haven't used a jig for a couple of years now. For my 80 degree bevel, I sharpen it on my scraper platform which is preset to the proper angle. There is minimal sweep, as in 1/2 inch gouge, and a straight edge across the nose would have less than 1/8 inch clearance on each side. I guess it is more ) shaped, but a bit flatter. I would never attempt to sharpen one like this in a jig, any more than I would a spindle roughing gouge.

robo hippy

[Jim Burr]

If you are happy and doing good work with what you have...why change? Mouse traps still catch mice.

[Steve Kubien]

How about this... I have no idea what angle my bowl gouges are ground at. Not a clue. I know I have a 5/8" P&N that is ground on a more "traditional" shape which I sometimes use near the bottom of bowls. It is different at the nose than the others. Heck, I've been known to grab it when roughing spindle blanks if my SRG is dull and I am too lazy to go to the grinder. Ya know what, it cuts just fine. In fact, they all do.

If you are having success and fun with what you have, don't change.

[Curt Fuller]

How about this... I have no idea what angle my bowl gouges are ground at. Not a clue. I know I have a 5/8" P&N that is ground on a more "traditional" shape which I sometimes use near the bottom of bowls. It is different at the nose than the others. Heck, I've been known to grab it when roughing spindle blanks if my SRG is dull and I am too lazy to go to the grinder. Ya know what, it cuts just fine. In fact, they all do.

If you are having success and fun with what you have, don't change.

After reading the replies to this post for the last few days I finally see one I can relate to. I have to be honest and say that I'm not even sure where you're measuring the angle. I hand grind all of my tools without a jig and I've developed a feel over the years for what works well for me. But I'm certain that the angle of my grinds varies from tip to wings, all being some variation of a fingernail grind. I'm sure I just adjust the angle of my tool presentation to the angle of my grind. Also, Mike Mahoney is the only big name professional turner I've ever had the opportunity to watch in action. He has such talent and skill that it would take a lot more than just using his tool grind to get his results. The guy is amazing.

[Nick Stagg]

Michael,

With your 60 degree grind your angle to the wood is much steeper than with a 40 degree grind and you're more likely to get the "bounce" on the outside of a bowl. The 40 degree gouge can be used on the outside of a bowl/vessel and two thirds of the way on the inside of a bowl. A steeper 50-60 degree grind can be used for the last third of the bowl, depending on its shape.

With the 40 degree grind all the energy/force is being applied to the wood being cut ahead of it; the wood that's left behind doesn't know its been cut. You'll get a superb finish right off the gouge with no need to resort to shear scraping or using a scraper on its side. Its especially good with soft, spalted, or other difficult woods.

A couple of tips that will help you with the steeper grind across the bottom: it won't pick up side grain very well so make sure you go deep enough with the 40 degree. Don't push the gouge, start with the handle across the ways of the lathe and when you pick up the cut, pull the gouge towards you. Its a swinging cut. Pushing it will make it skip and come off the bevel. Have the flute facing up when you finish the cut with the center of the gouge cutting the center of the bowl. Also, grind some of the heel off your bevel so it doesn't keep the tool off the work and leave ridges.... I do this to all my gouges. A roll back and forth on a coarse wheel will do it

Unfortunately, none of the grinding jigs will replicate the 40 degree grind; it has to be ground freehand using the flat platform, but its very easy to do.

Stuart Batty showed me how to grind it in the spring of 2005 and since then, in classes, and sawdust sessions I've put that grind on dozens of gouges for other turners.

Ill try and post a picture of it tomorrow

[Mark Levitski]

IMO, the angle of the grind has nothing to do with how the gouge cuts. I feel that this is a myth. The only thing the bevel angle does is define the relation of the cutting edge bevel to the handle/shaft axis.

Imagine a hinge or articulated joint between the bevel and the handle. One could adjust the bevel angle at this hinge instead of grinding a new and different-angled bevel. The cutting mechanics will be identical, only the handle orientation would change, and that is why people use different gouges for different forms.


Unfortunately, none of the grinding jigs will replicate the 40 degree grind
I regularly use my Wolverine vari-grind to produce a +/- 40* grind. I think you are referring (correctly) to a traditional grind with this statement. I use an Ellsworth-type configuration for the wings, but vary my bevel angles mostly for access to the piece.

The differences in cutting side-grain will come into play with traditional grind vs. swept-back. With the steeper wings of the traditional grind, it goes through end grain much cleaner. This grind works real well on the bottoms of bowls in lieu of a scraper.

Again, either the traditional or the swept-back can be ground steeper or flatter (i.e., 85* or 40*).

[Doug Thompson]

The only thing the bevel angle does is define the relation of the cutting edge bevel to the handle/shaft axis.

Bingo! Professionals use a grind to match what they are turning so don't try a deep bowl with a 40 degree grind.

[Reed Gray]

The most important angle to me is the shear angle. To me, this means the angle of the cutting edge as it is presented to the spinning wood. A pure scraping cut is a scraper flat on the tool rest. While this cut, with a gouge (flutes at 3 or 9 o'clock) or scraper is very effective for removing bulk, it does not leave a pretty surface. This is why it is called a roughing cut. When you are fine tuning the shape, and taking lighter cuts, it does okay. Across the bottom of a bowl, it does okay, but on the sides, since it is cutting through end grain and flat grain, and tends to pull, rather than slice through the fibers, it still leaves a rough surface. If you hold the tool up on edge at a 45 degree angle or more, the cuts get very clean because slices through the fiber, rather than pulling. For a bevel rubbing cut, the nose of a gouge is at more of a shear angle, and the wings are at more of a scraping angle. If you roll the flutes totally over,, drop the handle, and do a non bevel rubbing shear cut to clean things up, you have a high shear angle, and a clean cut. When you start to drop your handle when cutting and rubbing the bevel, you get more of a compound miter angle for crown molding, so I don't really know if a 40 degree bevel would still be the same here. Kind of confusing. The bevel does point the way, and learning where to point so you get the clean cut, and a smooth profile is a learning hurdle. I had a turner come over a few days back for some mentoring after Nick's demo for our club. After reshaping his gouges a bit (Benjaman's Best with wings ground straight up and micro thin), he was able to get good cuts, but wasn't able to keep the bevel pointing where he wanted it to go.

10,000 more times Grasshopper.

But teacher, that is what you said last time.

Well, 10,000 more times.

robo hippy

[Nick Stagg]

I probably should have explained myself more fully when I mentioned that the grinding jigs won't replicate the 40 degree grind that I was referring to.......they can't because they don't duplicate the side angles of the gouge. The nose is obviously no problem.

The bevel is 40, the wings angle back to the flute at 40, and their relationship to the inside of the flute is also at 40. It's not a "traditional" grind, nor does it have swept back wings. Go to You Tube and watch Mike Mahoney grind it and you'll have a better appreciation of what I'm trying to explain. Or, look in a tool catalog.

I thought I had explained well enough in my previous post that the 40 degree gouge will only go two thirds of the way down the inside of a bowl.... then you can use a gouge with a steeper grind and, if its a deep bowl, a gouge with a heavier cross section.

[Mark Levitski]

Maybe I'll make huge jumps in my turning knowledge and skills when................I get off dial-up and can watch videos :).

[Quinn McCarthy]

This has been an interesting thread to watch all weekend. Thanks

Quinn

[Ryan Baker]

After seeing a lot of people using 40 degree bevels, namely Mike Mahoney, I decided that seemed like a good idea to try and ground one of my gouges that way. I worked with it for a while. I hated it. It cut fine for what it was supposed to do, but I just couldn't get to like it. I reground it back to somewhere in the 50-60 degree range and I am much happier once again. Nothing wrong with the 40 degree thing if that works for you, but it's just not the grind for me.

[Roger Wilson]

Interesting set of 6 videos on youtube on this subject by Gary Gardner:

http://www.youtube.com/watch?v=9ljhd_WbAOw